Low threshold yttrium silicate laser glass with high damage threshold

ABSTRACT

Yttrium silicate laser glass having low thershold and high performance can be formed in all ceramic melting units. The glass is free of metallic inclusions and semi-conductive inclusions. The laser glass is doped with trivalent neodymium ions.

United States Patent Deeg et al. Oct. 2, 1973 LOW THRESHOLD YTTRIUM SILICATE [56] References Cited LASER GLASS WITH HIGH DAMAGE UNITED STATES PATENTS THRESHOLD 3,663,474 5/1972 Lee et al. 252/3014 F Filed:

inventors: Emil W. Deeg, Woodstock, Conn.;

Robert E. Graf, Southbridge, Mass.

Assignee: American Optical Corporation,

Southbridge, Mass.

Aug. 12, 1971 Appl. No.: 171,401

US. Cl 252/3014 F, 106/52 Int. Cl.... C09k 1/54, C03c 3/28, C030 3/04 Field of Search 252/3014 F; 106/52 Primary Examiner-Oscar R. Vertiz Assistant Examiner.l. Cooper Altorney-William C. Nealon et a].

[57] ABSTRACT Yttrium silicate laser glass having low thershold and 3 Claims, No Drawings 7 LOW THRESHOLD YTTRIUM SILICATE LASER GLASS WITH HIGH DAMAGE THRESHOLD When in operation, lasers produce tremendous amounts of energy and this energy internally of the The glass is of the high gain type with low threshold performance.

GENERAL DESCRIPTION OF INVENTION glass of the laser causes metallic and semi-conductive 5 Yttrium silicate laser glass according to the present inclusions to expand, move, vaporize, etc. thereby invention is fabricated according to the techniques decracking or causing the glass to explode. These probscribed and claimed in copending application No. lems are overcome according to the method of glass 63,593 identified above. In its broadest aspect, laser production taught in copending application No. 63,593 glass according to the present invention falls within the of Emil Deeg and Elias Snitzer. The application was l following ingredient ranges within the weight percent filed Aug. 13, 1970 and bears the title "Method of Prolisted. ducing Laser Glasses Having High Resistance to lnternal Damage and the Product Produced Thereby." This i'lz earth S53 application is now abandoned. The disclosure of that Y -20 application relating to fabrication of laser glasses is in- 32%: g g corporated herein by reference since the glasses of this Alfali'oxide invention are made according to the procedures and p r e set forth in that applicat on- The glass inherently has a minor but efiective amount It is also desirable to have laser glass characterized by of a fining agent. Any fining agent may be us d, E a low threshold. The glasses of this invention satisfy i (3 0 $1, 0 As,O;,. We prefer CeO,. The that requirement. It is also desirable to have glass charagent may unt to 0.5 to 2%.. 1% is preferred. Of acterized lOW fluorescent lifetime. The glasses Of this course, the overall theoretical weight percentage of ininvention a Satisfy this requirement gredients must be 100% although analytical analysis umerical ercenta es somewhat less or OBJECTS or lNVENTlON may p g greater than 100%. Incl am ng th object n advan ge f he Alternative alkali earth constituents in the foregoing present invention is to provide yttrium si l er examples may be a mixture. Likewise, the alkali oxide glasses with a high damage threshold, essentially no constituents may be a mixture. metallic or semi-conductive inclusions, and high gain. The preferred composition and the best mode now This and other objects and advantages of the invenknown for the practice of the invention is made from tion may be readily ascertained by referring to the fola batch having the constituents shown for example 5 in lowing description and examples wherein laser glass acthe following table:

7 TABLE l 2 3 4 5 6 7 8 SiO, 58.00 57.00 57.00. 53.00 58.00 58.00 37.14 39.63 Li 0 3.71 N516) 30.00 26.00 30.00 20.00 15.00 15.00 15.84 RbrO 24.75 C30 6.00 6.00 12.00 12.00 12.00 BaO 40.61 Alz n 2.00 2.00 2.00 3.71 3.96 Y,O3 2.00 7.00 9.00 9.00 9.00 9.00 11.12 11.36 CeO 1.00 1.00 1.00 1.00 1.00 1.00 Ndzoa 3.00 3.00 3.00 3.00 3.00 3.00 3.71 3.96

Melt size gm 50 gm 50 gm 50 gm 50 gm 2lbs. 11b. 11b. Crucible Pt." Pt. Pt. Pt. Pt. Pt. cerarniel' ceramic Relative lifetime 0.48 0.40 0.42 0.35 0.35 0.31 L s x seq .T ty e .lstme a asked ee am s. Hande ma eulqg sn 145 m 564T? crucible (note exceeded properties (Note total alkali 13.0 598C allowable limit of BaO) oxides Rb O and N320 ex- 10.5 660C ceecled allowable limit) 7.6 753 C.

iceramic is a mullite crucible of the Coors Company identified Cl-'C.

* "Pt is a platinum crucible.

cording to this invention is described. The resulting glass is shaped by such known techniques as casting, extruding, pressing or drawing.

DESCRIPTION OF INVENTION In general the composition of laser glasses made according to the invention contains ingredients in the following list within the weight percent listed.

(fining agent) 0.5 and 2 **Relative Lifetime is fluorescent lifetime determined in the following manner: an optically surfaced sample (preferably one cubic centimeter or less and having about a one centimeter square, optically polished surface) is exposed to a pulse of white light produced by a xenon flash lamp of the type normally used for laser experiments (choice of lamp is unimportant as long as same type of lamp is used in the comparison). The flash tube is driven by an electronic pulse short as compared to the expected lifetime. For example, if expected lifetime is 0.7 milliseconds, the lamp is driven at 0.07, about 10 times less. The samples fluoresce and fluorescence is measured by photo-electronic means and comparative value are determined. In our tests,

values of greater than 40 milliseconds are undesirable. It should be understood this test is an arbitrary means of comparing a group of samples. We assume that the curve of the decay of fluorescence intensity is a true exponential for the purpose of making fluorescent lifetime measurements. This is not really true for glass laser materials and the value of lifetime will vary depending where on the curve it has been measured. We do, however, still use the exponential decay formula to determine lifetime but the data are taken from the curve over some fixed time interval. The equation for exponential decay is:

and the variables are obtained from the curve. The values of I and I, are arbitrarily chosen as 3 X and 6 X 10 sec respectively. This allows the tail of the excitation light pulse to die down before the lifetime measurement is made so that no error will be introduced. These values of t, and I, must be adhered to closely when an accurate comparison of lifetimes is to be made. In our experience, as t, is allowed to increase, the measured value of lifetime increases. increases by a factor of 2 have been observed.

I, intensities of fluorescence at times t, and 1 respectively: 1' fluorescent lifetime.

Each of the above-stated batch compositions were prepared according to standard weighing and mixing procedures. To avoid dusting and to reduce volatilization losses of batch constituents during the reaction phase of the melt, all batches are pelletized. The batch was filled in portions of approximately 300 grams into a preheated mullite crucible at approximately l,400C. When the filling and reacting phase was completed, the melt was gradually cooled to approximately l,360C, at which temperature fining of the melt occurred. This phase lasted approximately 10.5 hours. The ceramic utensils were formed of high purity mullite, which is the preferred composition of the utensils, although high purity alumina and fused silica may also be utilized.

During the succeeding period of approximately 44 hours, the melt was homogenized and conditioned while the batch temperature was lowered to and then maintained at approximately l,l 10C. Throughout the SiO, 40-70 wt. Alkaline earth oxide 5-20 Y O, 5-20 Al,0, 0-l0 Nd,0, 0.5-6 Alkali oxide 5-30 effective amount of a fining agent. provided the total weight percent equals I00 weight percent, said glass having low threshold performance, being of the high gain type and being free of metallic and semi-conductive inclusions and reduced tendency towards microphase separation and devitrification.

2. Yttrium silicate laser glass according to claim 1 consisting essentially of:

SiOg 40-65 wt. an alkaline earth oxide selected from the group consisting of CaO, BaO, MgO, SrO and 5-20 mixtures Y,O; 5-20 M 0; 2-8 Nd,o, 0.5-5

an alkali oxide selected from the group consisting of Li,O, Na,O, K10, Rb o, 5-15 C810, and mixtures effective amount of a fining agent.

3. Yttrium silicate laser glass according to claim 1 having the following oxide analysis:

SIO, 58 wt. k CaO l2 Alzoa 2 Nd O; 3

CeO, 1 

2. Yttrium silicate laser glass according to claim 1 consisting essentially of: SiO2 40-65 wt. % an alkaline earth oxide selected from the group consisting of CaO, BaO, MgO, SrO and 5-20 mixtures Y2O35-20 Al2O3 2-8 Nd2O3 0.5-5 an alkali oxide selected from the group consisting of Li2O, Na2O, K2O, Rb2O, 5-15 Cs2O, and mixtures effective amount of a fining agent.
 3. Yttrium silicate laser glass according to claim 1 having the following oxide analysis: SiO258 wt. % CaO12 Y2O39 Al2O3 2 Nd2O33 Na2O15 CeO2 1 